sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Brownish-yellow, tan, and waxy greyish-white; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs
- Color
- Brownish-yellow, tan, and waxy greyish-white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 Mohs; Color: Brownish-yellow, tan, and waxy greyish-white; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic materials or chemical precipitation in sedimentary environments. Common as nodules in limestone or as water-worn pebbles in riverbeds.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used for landscaping, tumbled stones, and occasionally lapidary work.
Geological facts
This specimen shows the typical waxy luster and smooth, rounded water-worn edges of a river stone. The brownish-yellow coloration is often due to iron oxide (limonite) impurities.
Field identification & locations
Look for a smooth, waxy surface that cannot be scratched by a steel knife. It is frequently found in gravel deposits, river banks, and beaches worldwide.
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